Re: [PATCH 1/2] clk: mvebu: armada-37xx-periph: Fix switching CPU rate from 300Mhz to 1.2GHz

Stephen Boyd
2018-07-06T23:44:51Z

Quoting Gregory CLEMENT (2018-06-29 07:44:02)
> Hi,
>
> On mar., juin 19 2018, Gregory CLEMENT <gregory.clement@bootlin.com> wrote:
>
> > Switching the CPU from the L2 or L3 frequencies (300 and 200 Mhz
> > respectively) to L0 frequency (1.2 Ghz) requires a significant amount
> > of time to let VDD stabilize to the appropriate voltage. This amount of
> > time is large enough that it cannot be covered by the hardware
> > countdown register. Due to this, the CPU might start operating at L0
> > before the voltage is stabilized, leading to CPU stalls.
> >
> > To work around this problem, we prevent switching directly from the
> > L2/L3 frequencies to the L0 frequency, and instead switch to the L1
> > frequency in-between. The sequence therefore becomes:
> >
> > 1. First switch from L2/L3(200/300MHz) to L1(600MHZ)
> > 2. Sleep 20ms for stabling VDD voltage
> > 3. Then switch from L1(600MHZ) to L0(1200Mhz).
>
> Do you have any comment on this fix?
>

Looks good. Is it crashing right now? I can throw it into clk-fixes if
it's fixing pain.